1. Field of the Invention
This invention relates, in general, to mining tools and, more specifically, to mining drills and bits.
2. Description of the Prior Art
In the mining industry, Federal and State safety laws require that roof bolts be installed in the roof so as of each mine to provide support for the roof to prevent collapse or cave-in. The roof bolts generally comprise an elongated bolt having an expandible nut mounted at one end and a square plate mounted at the other end. The bolt is inserted into a hole drilled in the roof of the mine and the bolt is torqued to cause the nut to expand and anchor itself in the rock. The plate on the bottom of the bolt provides support for the roof of the mine to prevent collapse.
A variety of drills are commonly employed to form the holes in the roofs of mines. A typical drill has a cone-shaped head which removably receives a carbide insert or cutting bit and is formed to allow for removal of dirt and debris from the cutting area. The opposite end of the drill is inserted into a hollow bar which provides a means for rotating the bit. The bar, in turn, fits into a conventional drilling machine.
Such drills, while generally effective in forming holes in mine roofs which meet federal and state regulations for size tolerance and concentricity, are not without drawbacks. For one, it is not uncommon to have the bits undersized and the bars oversized which creates a misfit when the bit is inserted into the bar. During the drilling operation, the bit will wobble or move from side to side within the bar which imposes excessive force on the bit and leads to frequent breakage of the bit. In addition such movement often leads to a nonconcentric hole.
Another problem with previously devised mining drills used in mine roof operations arises when water is encountered during drilling. Under such conditions, the hole will shrink during drilling due to the pressure of the water which causes frequent breakage of the bit or separation of the bit from the bar within the hole. Further, the shrinkage leads to undersized holes which cannot receive the standard size roof bolt.
Thus, it would be desirable to provide a mining drill which overcomes the problems of previously devised mining drills. It would also be desirable to provide a mining drill which is particularly suited for use in forming holes in mine roofs. It would also be desirable to provide a mining drill which includes a bit and bar which can drill any depth hole and maintain close size tolerances and concentricity. Finally, it would be desirable to provide a mining drill which can maintain proper hole size under wet conditions.